JPH05329498A - Method for removing and recovering aluminum in sludge in water purification - Google Patents

Abstract

PURPOSE:To effectively utilize sludge in water purification as soil for growing crops and to enable the recycling of recovered aluminum as a flocculating agent by washing the sludge with hydrochloric acid or dilute hydrochloric acid, thereby recovering the soluble aluminum in the sludge. CONSTITUTION:The water from rivers is sterilized in a sterilizing tank 1 and is then introduced to a stirring basin 2 where polyaluminum chloride for waterworks is added as a flocculating agent to the water and the water is stirred. The flocs are sent to a floc forming basin 3 where the flocs are formed. The water contg. the flocs is sent to a settling basin 4 where the water is held still. Consequently, the sludge in water purification is formed. This sludge is sent into a sludge thickening tank 5 and is thickened. The sludge is further sent to a dehydrating machine 6. The dilute hydrochloric acid for neutralization is added to the dehydrating machine 6, by which the sludge is washed with the dilute hydrochloric acid simultaneously with the dehydration of the sludge. As a result, the soluble aluminum in the sludge is removed and the recovered aluminum is treated with a treating device 7 and is recovered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the above coagulation in sludge (referred to as "purified water sludge" throughout the specification) produced by precipitating turbid components of water from a river at a water purification plant by adding a coagulant. The present invention relates to a method for removing and recovering aluminum content derived from the agent from purified water sludge.

[0002]

Prior Art and Problems to be Solved
It is a clay composed mainly of ₂ , Al _{2 O 3} and Fe _{2 O 3} , which is currently disposed of by landfill. However, in recent years, it is becoming more and more difficult to secure a landfill disposal site, and a measure for effectively utilizing the purified water sludge for other purposes is desired.

The coagulant added to river water at a water purification plant is polyaluminum chloride (PAC) JIS K147 for water supply.
5 (1978). Therefore, if the purified water sludge containing this coagulant is used as it is as soil for agriculture, P
Soluble aluminum in AC reacts with phosphate fertilizers, resulting in soils that are phosphorus deficient and inhibit crop growth. Therefore, a technique for removing PAC from purified water sludge is required.

Conventionally, there are several methods of recovering aluminum sulfate in the treatment of purified water sludge, but there is no example of recovering an aluminum chloride-based coagulant.

There is also a method in which soluble aluminum is fixed by drying and firing purified water sludge and the treated sludge is effectively used as soil. However, this method consumes a large amount of fuel for firing, and aluminum is used. However, there is a drawback that it cannot be collected.

An object of the present invention is to remove soluble aluminum of polyaluminum chloride flocculant contained in purified water sludge, effectively utilize the purified sludge as soil for growing crops, and reuse recovered aluminum as flocculant. To provide a way to do.

[0007]

The present invention has been devised to achieve the above object and is characterized by recovering soluble aluminum in sludge by washing purified water sludge with hydrochloric acid or dilute hydrochloric acid. This is a method for removing and recovering aluminum from purified water sludge.

[0008] The purified water sludge to be treated is washed with hydrochloric acid or dilute hydrochloric acid at the same time as it is concentrated in a concentrating tank or after being concentrated, or at the same time as being dehydrated by a dehydrator or after being dehydrated. Simultaneously with or after dehydration, dilute hydrochloric acid is preferably used.

[0009]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

In the water purification plant, the water taken from the river is guided to the sterilization tank (1), and chlorine is added to this water to sterilize it. This water is then led to a stirring pond (2), where water polyaluminum chloride is added as a coagulant to the water,
The water is stirred. This water is then sent to the floc pond (3) where flocs are formed by the flocculant, then the water containing flocs is sent to the settling pond (4) and allowed to stand. As a result, turbid components in water are precipitated and purified water sludge is produced. This sludge is then sent to the sludge thickening tank (5) for concentration, and the concentrated sludge is further sent to the dehydrator (6). Diluted hydrochloric acid for neutralization is injected into the dehydrator (6), and the sludge is dehydrated and simultaneously washed with diluted hydrochloric acid by driving the dehydrator (6).

By this acid washing, soluble aluminum in the sludge is removed, and the obtained washed sludge is effectively used as soil for growing agricultural products. On the other hand, the recovered aluminum is treated in the treatment device (7) and reused as a flocculant.

The turbidity-removed water obtained in the sedimentation basin (4) is filtered in the rapid filtration basin (8) and then stored in the water purification basin (9).

Soluble aluminum in the purified water dewatered sludge before treatment is about 45,000 mg per kg of dry sludge, and about 500 mg in general soil. Therefore, in order to reduce the content of soluble aluminum in purified water sludge to the value of general soil, 9% soluble aluminum in purified water sludge should be used.
It should be removed to close to 9% (in which case most of the aluminum from the added polyaluminum chloride condensing agent will be recovered). As described above, the soluble aluminum from the dehydrated sludge using the polyaluminum chloride flocculant was washed and removed with a dilute acid. After washing the dehydrated sludge on the filter paper with 0.5N hydrochloric acid, the sludge on the filter paper was dried and the soluble aluminum was eluted and analyzed.
It became 500 mg or less per gram.

[0014]

According to the present invention, the purified sludge is washed with hydrochloric acid or dilute hydrochloric acid to remove the soluble aluminum of the polyaluminum chloride flocculant contained in the purified water sludge, and the purified sludge is used as a soil for growing agricultural crops. The recovered aluminum can be reused as a flocculant.

[Brief description of drawings]

FIG. 1 is a flow chart showing an embodiment of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kanshi Ota, 5-3-8 Nishi Kujo, Konohana-ku, Osaka City, Hitachi Shipbuilding Co., Ltd. (72) Naoko Hirata 5-28, Nishi Kujo, Konohana-ku, Osaka Issue Hitachi Shipbuilding Co., Ltd.

Claims (1)

[Claims] 1. A method for removing and recovering aluminum in purified water sludge, which comprises recovering soluble aluminum in the sludge by washing the purified water sludge with hydrochloric acid or dilute hydrochloric acid.